Electrical contacting device



Nov. 8, 1932. P. G. SWARS 11,86,75fi' ELECTRICAL CONTACTING DEVICE Filed NOV. 12. 1928 INVENTOR M a*- fly Aka My Patented UNITED PAUL G. SWARS, 01E PITTSBURGH, PENNSYLVANIA nnncrnrcar. oonracrme nn'vro'n Application filed November 12, 1928. Serial No. 318,886.

. conducting members.

current conducting members,

faces.

In transferring electrical energy between the eficiency of the contact depends in part upon the areas of engagement between the conducting parts, and upon the pressure exerted betweenthe parts. Where uneven contact exists between the difierent portions of engaging current conducting members, there is an uneven distribution of current about the contacting The unequal distribution of current causes localized heated spots. Where spaces exist between the contacting surfaces, the electrical resistance of the connection is increased with a resultant increase of heating. In some cases the localized heating has been sufficiently great to ruin the temper of the electrical conducting'material and adjacent reinforcing members. 1

The current conducting materials most commonly used are copper and aluminum. Both of these materials are relatively soft and do not possess sufiicient resistance to bending forces to enable them to keep their shapes and thereby preserve good contacting surfaces. This is'especially true after the current conducting members have once been subjected to heavy eleetricaLcurrents which are liable to anneal the current conducting mem-,

bers. For reinforcing thecurrent conducting members and supplying suflicient pressure to insure good electrical contact between current conducting surfaces, reinforcing or bracing strips have been applied along the surfaces of the current conducting members opposite their current transferring surfaces. Such reinforcing members are often mounted on the same base as the current conducting members andare freguently in parallel circuit to one or more 0 the current conducting members.

Reinforcing members, when in parallel circuit with the current conducting members,

are liable to conduct a. considerable amount of current unless provision is made for 1ncreasmg the electrlcal resistance of the current path through such reinforcing members. Under normal loads, the current traversing the reinforcing members may not be excessive, but under conditions of short-circuit or current surge, where the current is greatly increased, there is danger of the reinforcing members being excessively heated and annealed at a time when full contact pressure is most needed. For increasing the resistance of the electrical members, it has heretofore been proposed to insert sheets of electrical insulating material between each current conducting member and cooperating reinforcing member.

The presence of sheets of fabricated inca sulating material in electrical contacting devices virtually necessitates that the contacting device shall be used in-doors in comparatively dry places. Most fabricated insulating materials deteriorate rapidly when 79 exposed to the actions of gases and fumes such as are present in the atmosphere in most industrial communities' Such material cannot be used when continuously exposed to moist atmosphere such as is present around large bodies of water, or in many industrial plants, as the insulating material tends to absorb water and become a conductor. It has been repeatedly demonstrated that the best non-conducting heat dissipators for ex- 80 posed work are air andinert gases. For inclosed work the best non-conducting heat dissipators are high-fire test oils or non-conducting liquids, such as carbon-tetrachloride.

Where a body of any ofthe foregoing nonconducting heat dissipators can be positioned between portions of a current-carrying member and a reinforcing member, the presence of the body of non-conducting heat dissipator tends to reduce the amount of current traversing the reinforcing members.

I provide a reinforcing or tensioning means for electrical contacts in which a metallicreinforcing member directly engages a current conducting member. The metallic reinforcing memberis shaped to provide a large volume of. a non-conducting and heat-dissipating medium between its surface and the surface of the current conducting member, while maintaining a well distributed and firm 1 path through reinforcing cc the current conducting member.

The space is filled with a non-conducting medium, which is permitted to circulate between the surface of the reinforcing member and the electrical conducting member, thereby dissipating such heat as is developed.

In order to increase the electrical resistance of a current conducting path through the reinforcingmember,the projections are made of relatively small cross-sectional areas near their points of contact with the current conducting member. In case excessive current tends to traverse the projections, they become heated at their points of contact. However, by reason of the limited cross-sectional areas of the projections, they offer considerable electrical resistance, which resistance increases as their temperature increases. Accordingly, the heated portions of the projections are limited for short. distances from their outer ends. As an insulating medium is continuously circulating past the projections, the heat is quickly dissipated and the body of the reinforcing member is kept at a temperature to revent its becomin annealed.

he accompanying rawing illustrates certain present preferred embodiments of the invention in which Figure 'l is an elevational view of an electrical clip and cooperating knife blade involving my invention 5 Fig. 2 is a similar view showing a modified form of clip; 1

Fig. 3 is a similar view showing a modified form of the invention adapted for use with circular conducting members;

Fig. 4 is a diagrammatic view of a form of the invention adapted for use with drum contacts;

' Fig. 5 is a View illustrating a brush and brush-holder provided with m invention;

Figs. 6, 7 and 8 illustrate -di erent forms of reinforcing members, and

Fig. 9 is a perspective view of a further modification of the invention.

Referring to Fig. 1, an electrical clip 2 is provided with a base 4 from which statlonary contacting jaws 5 extend. The jaws 5 are copper and extend in parallelism from the base {1. The jaws 5 are spaced apart far enough to permit the entrance of a blade 6 of current conducting material, such as copper. The blade 6 is illustrative of a knife in a knife blade switch, or the end of a fuse having a flat current conducting extension.

In order to provide a uniform engagement between the jaws 5 and the blade 6, reinforcing or tensioning members 7 in the form of metallic springs, preferably of ferrous metal, are secured to the base 4 by screws 8 It is to be understood that other forms of securing means may be substituted for the screws 8 if desired. The reinforcin members 7 are provided with a plurality 0% projections 9 along their inner faces.

It is to be understood that the projections on the reinforcing members may be formed by a punch operation, riveting, screw fitting, welding, and the like.

The presence of the projections 9 between the reinforcing members 7 and the jaws 5 provides spaces through which an insulating medium. such as air, an inert gas, or a nonconductive liquid, such as oil or carbon tetrachloride, may circulate. .The circulation of the insulating medium dissipates the heat developed during the o eration of the contact, thereby preventing t e reinforcing members from becoming excessively heated and annealed.

The projections 9 are of relatively small cross-sectional area at their outer ends. The

"number of the projections is such that a firm and uniformly distributed pressure is transeach rib offers a considerable resistance to.

the passage of electrical current. Should an excessive amount of current tend to traverse the projections 9, they become heated, which increases their resistance to the transmission of current. Due to their small cross-sectional areas, the circulating medium rapidly dissipates such heat as is developed. The presence of the heated portions at the ends of the projections does not impair the reinforcing and tensioning characteristics of the members 7.

As illustrated in Figs. 6, 7 and 8, the projections 9 may be any one of several forms.

In Fig. 6 projections 9a of small cone-like shape are struck up from the body of the reinforcing member. In Fig. 7 elongated projections'9b are struck up from the body of a reinforcing member 7a. The projections 96 are arranged to extend radially from a common center.

Referring to Fig. 8, a metallic screen 10 is secured between a conductor and a reinforcing member 70. The screen may be secured to the reinforcing member in any desired manner, as by spot welding. The screen may be welded to the conductor if desired.

Referring to Fig. 2, the invention is applicable to a contact device having a single stationary contact member 11 mounted on a base 12. A second current conducting member 13 bears against the inner edge of the stationary contact member '11. A resilient member 14 ha ring projections 15 formed thereon bears against the second surface of the conducting member 13.

Referring to Fig. 3, the invention is appllcable to circular conducting members 16 such as the ends of fuse clips, by providing the responding to the clips 17 shown in Fi asserts customary curved clips 17 with curved reinforcing members 18 secured to a common base 20 for the clips 17. The reinforcing members 18 are provided with projectlo 19 corresponding to the projections 9 sho in Fig. 1.

Referring to Fig. 4, the invention s applicable to drum type contacting devices. current conducting drum 21 is mounted in supports 22.

A contacting finger 24 engages a ort on of the surface of the drum 21. A rein orcing member 25 bears against the outer face of the finger 24:. The inner surface of the reinforcing member 25 is provided with pro ections 26 which engage the outer surface of the finger 24. The projections 26 perform the same functions as the projections 9 shown in Fig. 1.

Referring to Fig. 5, the invention is applicable to brushholders. A brushholder 27 encloses a brush 28 against the outer end of which a reinforcing member 29 bears. Projections 30 on the inner surface of the reinforcing member 29 engage the outer end of the brush 28.

In Figure 9 I have shown a modification of the invention, in which clips 17a, corre 3, are provided with projections 19a WhlCh engage the surface of a reinforcing member 18a having substantially a plain surface.

While I have shown and described certain present preferred embodiments of the invention, it is to be understood that the invention may be otherwise embodied within the spirit of the invention and the scope of the appended claims.

I claim:

1. In a switch, the combination with a movable blade, and jaws adapted to frictionally engage said blade when in closed position, of

leaf springs for urging said jaws into engagement with said blade, having high electrical resistance and a plurality of sharp points engaging said jaws.

2. The combination with a contact member adapted to frictionally' engage a conductor, of a reinforcing member for urging the contact member into firm engagement with the conductor, and spaced projections on one of said members for transmitting the efi'ect of the reinforcing member to the contact member.

In testimony whereof I have hereunto my hand.

' PAUL G. SWARS. 

